1. Technical Field
The present invention relates to a method for printing in a draft mode of a serial printer, and particularly to an improved method for printing in a draft mode of a serial printer which is capable of printing by aligning dots to be printed in a predetermined form according to the number of dots corresponding to data to be printed when bidirectional printing in a draft mode.
2. Related Art
Conventional printer such as a dot matrix printer, inkjet printer and plotter includes a printhead having an array of nozzles mounted on a carriage for printing a plurality of rows of dots in a single scan of a movable print carriage across a printable medium. Typical printer prints information serially one letter per unit time and can be unidirectional or bidirectional. Bidirectional printer can print information on a printable medium in both directions, that is, from left to right of a first row, and then from right to left of a second row next to the first row. As a result, a printing speed of bidirectional printer is two times faster than that of a unidirectional printer which can only print information in one direction and the carriage must be returned to a starting position for each row.
Many contemporary serial printers are provided with a so-called draft mode for rapid printing in which the number of dots or the rejection ink from a nozzle is reduced, for example, to half the number of dots used to make a character pattern under a normal mode. Exemplars of contemporary printers operable both in a draft mode and a normal mode of printing are disclosed in U.S. Pat. No. 4,586,835 for Printer For Printing Characters In Two Alternative Print Qualities issued to Alexander et al., U.S. Pat. No. 4,650,351 for Thermal Printer issued to Engle et al., U.S. Pat. No. 4,728,968 for Arrangement of Discharge Openings In A Printhead Of A Multi-Color Ink Printer issued to Hillman et al., U.S. Pat. No. 4,969,758 for Method Of Improving The Printing Speed Of Impact Dot Printer Printing In A Near Letter Quality Mode issued to Sanders, Jr. et al., and U.S. Pat. No. 5,198,833 for Variable Density Ink-Jet Dot Printer issued to Kubota, and U.S. Pat. No. 5,291,824 for Dot Line Printer Having Ordinary Low Dot And High Dot Density Printing Modes issued to Matsumoto et al. Generally, when the draft mode is selected for high speed printing in those serial printers, printing operation is performed by excluding a certain dot unconditionally. For example, when the dots are adjacent to data to be printed, one dot is printed and a next dot is not printed. Accordingly, when the number of the adjacent dots is an odd number, the vertical lines are aligned. However, when the number of the adjacent dots is an even number, the vertical lines are not properly aligned. As a result, contemporary printers which are operable in a draft mode experience a problem in that data (i.e., font or image) to be printed is refracted when performing bidirectional printing in the draft mode, as the number of dots included in the data to be printed can be both an even number and an odd number.